Ovonic Unified Memories (OUMs) are known as nonvolatile storage devices whose information read-out is achieved by detecting changes in resistance characteristics. OUMs use chalcogenide compounds whose resistance characteristics change significantly between crystalline and amorphous structures. Chalcogenide compounds are also adopted in phase-change optical disks such as DVD-RAM.
A recently known technique employs a nonvolatile memory device that utilizes a transition-metal oxide film of NiO, V2O5, ZnO, Nb2O5, TiO2, WO3, or CoO as a data-storage material layer, taking use of transition-metal oxide films' property of showing a rapid increase or decrease in resistance within a given voltage range. The resistance characteristics of the transition-metal oxide film is controlled by addressing each data-storage material layer with a transistor or the like, which is provided for each of the data-storage material layers, and applying a predetermined voltage hysteresis. The information held in the data-storage material layers is read out by detecting the resistance characteristics (see Patent Document 1).
A technique for forming memory elements is also known, in which the ferroelectric material Pr0.7Ca0.3MnO3 is used as a data-storage layer. The resistance characteristics of the layer are varied by a factor of about 10 to 1,000 by switching the voltage applied on the data-storage layer of the ferroelectric material to positive/negative within a predetermined magnitude, after which the resistance characteristics are detected (see Non-Patent Document 1).
The switching phenomenon of resistance characteristics between 100 and 200Ω and between 10 and 20Ω in a nickel oxide thin-film formed by exposing a nickel substrate to an oxygen atmosphere has been reported to be basically consistent with calculated results obtained under the assumption of the formation and break of Ni fiber filaments formed in a NiO matrix (see Non-Patent Document 2).    Patent Document 1 Japanese Patent Application Kokai Publication No. (JP-A) 2004-363604 (unexamined, published Japanese patent application)    Non-Patent Document 1 Applied Physics Letters, Vol. 76, No. 19 (2000), pp. 2749-2751    Non-Patent Document 2 Solid-State Electronics, Vol. 7 (1964), pp. 785-797